diff --git a/src/openrct2/world/Surface.cpp b/src/openrct2/world/Surface.cpp
index ae4d6c6ebb..4bfaf83a14 100644
--- a/src/openrct2/world/Surface.cpp
+++ b/src/openrct2/world/Surface.cpp
@@ -213,5 +213,5 @@ uint8_t SurfaceElement::GetSlope() const
 void SurfaceElement::SetSlope(uint8_t newSlope)
 {
     slope &= ~TILE_ELEMENT_SURFACE_SLOPE_MASK;
-    slope |= (newSlope | TILE_ELEMENT_SURFACE_SLOPE_MASK);
-}
\ No newline at end of file
+    slope |= (newSlope & TILE_ELEMENT_SURFACE_SLOPE_MASK);
+}